Novel silver complexing agents

ABSTRACT

There are described photographic products, processes and compositions wherein cyclic crown ether ligands are utilized as silver halide solvents. Also disclosed are novel cyclic crown ether ligands.

BACKGROUND OF THE INVENTION

This application relates generally to photography and more particularlyto photographic products, processes and compositions which includecyclic crown ether ligands as silver halide solvents.

Photographic processing compositions capable of forming water-solublecomplex silver salts are known to be useful in many types of silverhalide photography. In conventional or "tray" development, it iscustomary to fix the developed silver halide emulsion by applying asolution of silver halide solvent, i.e., silver halide complexing agentwhich forms a water-soluble silver complex with the residual silverhalide. The water-soluble silver complex thus formed and excess silverhalide solvent are then removed from the developed and fixed emulsion bywashing with water.

Silver halide solvents also have been employed in monobaths where asingle processing composition containing a silver halide developingagent in addition to the silver halide solvent is utilized for bothdeveloping and fixing an exposed photosensitive silver halide layer.Silver halide solvents also have been employed in diffusion transferphotographic processes. Such processes are now well known in the art;see for example, U.S. Pat. Nos. 2,543,181; 2,647,056; 2,983,606; etc. Inprocesses of this type, an exposed silver halide emulsion is treatedwith a processing composition whereby the exposed silver halide emulsionis developed and an imagewise distribution of diffusible image-formingcomponents is formed in the unexposed and undeveloped portions of thesilver halide emulsion. This distribution of image-forming components istransferred by imbibition to an image-receiving stratum in superposedrelationship with the silver halide emulsion to provide the desiredtransfer image. In diffusion transfer processes where a silver transferimage is formed, processing is effected in the presence of a silverhalide solvent which forms a diffusible complex with the undevelopedsilver halide. The soluble silver complex thus formed diffuses to thesuperposed image-receiving layer where the transferred silver ions aredeposited as metallic silver to provide the silver transfer image. Inpreparing silver prints in this manner, the image-receiving elementpreferably includes a silver precipitating agent, for example, heavymetal sulfides and selenides as described in U.S. Pat. No. 2,698,237.

The present invention is concerned with new photographic compositions,processes and products as well as novel silver halide solvents.

SUMMARY OF THE INVENTION

It is therefore the object of this invention to provide photographicproducts, processes and compositions wherein cyclic crown ether ligandsare utilized as silver halide solvents.

It is another object to provide novel cyclic crown ether ligands.

BRIEF SUMMARY OF THE INVENTION

These and other objects and advantages of the invention are accomplishedby providing photographic products, processes and compositions whichinclude, as silver halide solvents, at least one silver complexingcompound which is represented by the structural formula ##STR1## wherein

X may be selected from the group consisting of oxygen, nitrogen, sulfur,phosphorous and selenium;

R₁ and R₂ may be the same or different and may be H, alkyl,hydroxyalkyl, alkoxyalkyl or aminoalkyl, preferably having from two tosix carbon atoms, ##STR2## wherein

R₄ may be H, alkyl, alkoxy, or --NO₂ and R₅ may be H, alkyl, alkoxy oralkoxyalkyl; and

when X is --N--, R₃ may be H, alkyl, hydroxyalkyl, alkoxyalkyl oraminoalkyl, preferably having from two to six carbon atoms, ##STR3##wherein R₆ may be H, alkyl, cyano or ##STR4## wherein R₇ may be H oralkyl.

The compound wherein X is oxgyen and R₁ and R₂ are both hydrogen isdisclosed in Tetrahedron Letters, Pelissard and Louis page 4589 (1972).The other compounds which are within the general formula are per senovel compounds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One class of specific preferred silver complexing compounds which aresuitable for use according to the invention is represented by thegeneral formula ##STR5## wherein R₁ and R₂ are as described in Table I

                  TABLE I                                                         ______________________________________                                        Compound R.sub.1         R.sub.2                                              ______________________________________                                        A        H               H                                                    B        CH.sub.3        CH.sub.3                                                       ##STR6##       H                                                    D                                                                                       ##STR7##                                                                                      ##STR8##                                            E                                                                                       ##STR9##       H                                                    F                                                                                       ##STR10##                                                                                     ##STR11##                                           G                                                                                       ##STR12##                                                                                     ##STR13##                                           H                                                                                       ##STR14##      H                                                    ______________________________________                                    

Other specific preferred silver complexing compounds which are suitablefor use according to the invention are represented by the followingformulas: ##STR15##

Compounds A, B, I, J and L are stable in an alkaline environment, have amelting point less than about 50° and the log of the stability constant(β) for a 1:1 complex of the complexing agent with silver is at leastabout 10.5. By "stable in an alkaline environment" is meant that thesilver complexing agent retains at least 75% of its silver complexingability after being in a 1 N sodium hydroxide solution for twenty-fourhours at room temperature. These preferred complexing agents can be usedin a diffusion transfer photographic method for making positivetransparencies, without washing, which are substantially completely freeof crystals. The method is described and claimed in applicants'copending application Ser. No. 080,349, filed on even date herewith.Accordingly, these compounds are the preferred silver complexing agentsof the invention.

Compound A may be synthesized according to the method described inTetrahedron Letters, 45, pp 4589-4592 (1972). The pentadentatemacrocyclic ligands B, I, J and L can be prepared by reactingN,N'-dimethyl-N,N'bis(2-mercaptoethyl) ethylenediamine [for itspreparation see J. Amer. Chem. Soc., 98, page 6951 (1976)] with (Cl CH₂CH₂)₂ X (where X may be O, N--Me, NH or S) in a suspension of sodiumhydride in tetradydrofuran. Compounds such as C--H may be prepared fromcompound A by reaction with appropriate acyl halides. Similarly,compound K may be prepared from compound J by reaction withp-nitrophenyl chloroformate. The desired ligands can be separated fromthe crude reaction products by first treating their methanol solutionwith silver thiocyanate to form the 1:1 ligand-silver thiocyanatecomplex which preferentially crystallizes from solution while theimpurities remain in the filtrate. Recrystallization of the complexfollowed by precipitation of silver as silver sulfide with hydrogensulfide and liberation of the free ligand by passing an aqueous solutionof the resulting thiocyanic acid complex through an anion exchangecolumn provides essentially pure samples of the ligands. Alternativelypurification can be effected by chromatography of the crude productmixture on silica gel, a more time consuming procedure.

As mentioned previously, the compounds represented by the generalformula are useful as silver complexing agents in photography. The logof the stability constant (β) for the 1:1 complex of various preferredcompounds is shown in Table II. The stability constants were determinedby potentiometry, i.e, by titrating the ligand with a standardizedsolution of silver perchlorate in mildly alkaline, constant pH, constantionic strength medium (0.05 M NaOH, 0.10 M NaClO₄). All solutions andtitrants were prepared carbonate free and with an ionic strength of 0.1(NaClO₄) except when the perchlorate salt of the complex was found to beinsoluble. In those cases perchlorate was omitted from the system. Anargon atmosphere was used throughout. The indicating electrode was asilver specific ion type used in conjunction with a sleeve type doublejunction Ag/AgCl reference electrode.

                  TABLE II                                                        ______________________________________                                        Compound          Log β                                                  ______________________________________                                        A                 11.37 ± .01                                              B                 11.84 ± .01                                              I                 12.30 ± .01                                               J*               11.98 ± .02                                              L                 11.84 ± .02                                              ______________________________________                                         *No perchlorate was added                                                

In formulating photographic processing compositions utilizing theabove-described compounds, the compounds may be used singly or inadmixure with each other or with other silver halide solvents. The totalamount employed may vary widely depending upon the particularphotographic system and should be used, for example, in a quantitysufficient for fixing a developed negative in conventional "tray"processing or in a quantity sufficient to give a satisfactory transferprint in diffusion transfer processes under the particular processingconditions employed.

Though the silver halide solvents of the present invention are broadlyuseful in a variety of photographic processes of the type in whichwater-soluble silver complexes are formed from the unreduced silverhalide of a photoexposed and at least partially developed silver halidestratum, they find particular utility in diffusion transfer processes. Acomposition embodying the present invention specifically suitable foruse in the production of transfer images comprises, in addition to thesilver complexing agents of the above-described type, a suitable silverhalide developing agent. Examples of developing agents that may beemployed include hydroquinone and substituted hydroquinones, such astertiary butyl hydroquinone, 2,5-dimethyl hydroquinone,methoxyhydroquinone, ethoxyhydroquinone, chlorohydroquinone, pyrogalloland catechols, such as catechol, 4-phenyl catechol and tertiary butylcatechol; aminophenols, such as 2,4,6-triamino-orthocresol;1,4-diaminobenzenes, such as p-phenylenediamine, 1,2,4 triaminobenzeneand 4-amino-2-methyl-N,N-diethylaniline; ascorbic acid and itsderivatives, such as ascorbic acid, isoascorbic acid and5,6-isopropylidene ascorbic acid, and other enediols, such astetramethyl reductic acid; and hydroxylamines, such asN,N-di-(2-ethoxyethyl)hydroxylamine andN,N-di(2-methoxyethoxyethyl)hydroxylamine.

In diffusion transfer processes, the processing composition, if it is tobe applied to the emulsion by being spread thereon in a thin layer, alsousually includes a viscosity-imparting reagent. The processingcomposition may comprise, for example, one or more silver halidesolvents of the present invention, one or more conventional developingagents such as those enumerated above, an alkali such as sodiumhydroxide or potassium hydroxide and a viscosity-imparting reagent suchas a high molecular weight polymer, e.g., sodium carboxymethyl celluloseor hydroxyethyl cellulose.

In one such transfer process, the processing solution is applied in auniformly thin layer between the superposed surfaces of a photoexposedphotosensitive element and an image-receiving element, for example, byadvancing the elements between a pair of pressure-applying rollers. Theelements are maintained in superposed relation for a predeterminedperiod, preferably for a duration of 15 to 120 seconds, during whichexposed silver halide is reduced to silver and unreduced silver halideforms a water-soluble, complex salt which diffuses through the layer ofsolution to the image-receiving element, there to be reduced to anargental image. At the end of this period, the silver halide element isseparated from the image-receiving element. Materials useful in such atransfer process are well known in the art.

The photosensitive element may be any of those conventionally used insilver diffusion transfer processes and generally comprises a silverhalide emulsion carried on a base, e.g., glass, paper or plastic film.The silver halide may be a silver chloride, iodide, bromide,iodobromide, chlorobromide, etc. The binder for the halide, thoughusually gelatin, may be a suitable polymer such as polyvinyl alcohol,polyvinyl pyrrolidone and their copolymers.

The image-receiving element preferably includes certain materials, thepresence of which, during the transfer process has a desirable effect onthe amount and character of silver precipitated on the image-receivingelement. Materials of this type are known in the art.

Separating of the silver halide element from the image-receiving elementmay be controlled so that the layer of processing composition is removedfrom the image-receiving element or the layer of the processingcomposition is caused to remain in contact with the image-receivingelement, e.g., to provide it with a protective coating. Techniques whichenable such results to be accomplished as desired are described in U.S.Pat. No. 2,647,054. In general, the processing reagents are selected sothat traces remaining after the solidified processing layer has beenseparated from the silver image or which remain in said layer adhered asa protective coating on the silver image, as indicated above, arecolorless or pale, so as not to appreciably affect the appearance of theimage and to have little or no tendency to adversely react with thesilver image.

The silver halide solvents of the present invention also may be employedin diffusion transfer processes adapted to provide positive silvertransfer images which may be viewed as positive transparencies withoutbeing separated from the developed negative silver image including suchprocesses adapted for use in forming additive color projection positiveimages. Diffusion transfer processes of this type are known in the art.See, for example, U.S. Pat. Nos. 3,536,488, 3,615,428, and 3,894,871.The subject compounds also find utility in silver halide solvents indiffusion transfer processes utilizing the properties of the imagewisedistribution of silver ions in the soluble silver complex made availablein the undeveloped and partially developed areas of a silver halideemulsion to liberate a reagent, e.g., a dye in an imagewise fashion, asdescribed in U.S. Pat. No. 3,719,489.

As noted above, in diffusion transfer film units the negative componentcomprising at least one photosensitive layer and the positive componentcomprising an image-receiving layer may be in separate sheet-likeelements which are brought together during processing and thereaftereither retained together as the final print or separated following imageformation.

Rather than the photosensitive layer and the image-receiving layer beingin separate elements, they may be in the same element. In one such filmunit, the image-receiving layer is coated on a support and thephotosensitive layer is coated on the upper surface of theimage-receiving layer. The liquid processing composition is appliedbetween the combined negative-positive element and a second sheet-likeelement or spreading sheet which assists in spreading the liquidcomposition in a uniform layer adjacent to the surface of thephotosensitive layer.

Still other film units are those where the negative and positivecomponents together may comprise a unitary structure wherein theimage-receiving layer carrying the transfer image is not separated fromthe developed photosensitive layer(s) after processing but bothcomponents are retained together as a permanent laminate. Such filmunits include those for providing positive silver transfer images whichmay be viewed as positive color transparencies, such as, those describedin U.S. Pat. No. 3,894,871. Other integral film units also include thoseadapted for forming a transfer image, in color or in black and white,viewable by reflected rather than by transmitted light. In addition tothe aforementioned photosensitive layer(s) and image-receiving layer,such film units include means for providing a reflecting layer betweenthe image-receiving and photosensitive layer(s) in order to mask thedeveloped photosensitive layer(s) and to provide a white background forviewing the transfer image. This reflecting layer may comprise apreformed layer of a reflecting agent included in the film unit or thereflecting agent may be provided subsequent to photoexposure, forexample, by including the reflecting agent in the processingcomposition. In addition to these layers, the laminate usually includesdimensionally stable outer layers or supports, at least one of which istransparent so that the resulting transfer image may be viewed byreflection against the background provided by the light-reflectinglayer. Integral negative-positive film units wherein the photosensitiveand image-receiving layers are retained as a permanent laminate afterprocessing are described, for example, in U.S. Pat. Nos. 3,415,644;3,647,437 and 3,594,165.

It will be appreciated that in the formation of color transfer images, adye image-providing material such as the compounds of U.S. Pat. No.3,719,489 may be associated with the photosensitive silver halide layeror layers of the negative component.

The diffusion transfer film units described above are employed inconjunction with means, such as, a rupturable container containing therequisite processing composition and adapted upon application ofpressure of applying its contents to develop the imagewise exposed filmunit.

To illustrate the utility of the above-described compounds asphotographic silver halide complexing agents, certain of the compoundswere incorporated in photographic processing composition which were thenemployed in a photographic method. In one such illustrative showing afilm unit was prepared comprising a transparent polyester film basecarrying on one surface an additive color screen of approximately 1000triplets per inch of red, blue and green filter screen elements inrepetitive side by side relationship; an approximately 4 micron thickpolyvinylidene chloride barrier layer; a nucleating layer comprising0.23 mg/ft² of palladium nuclei (as metal), 0.29 mg/ft² of gelatin, 0.35mg/ft² of tin (as metal) and 0.47 mg/ft² of total chloride (associatedwith Pd and Sn); an interlayer of 2.21 mgs/ft² of deacetylated chitin,0.645 mg/ft² of copper acetate (dihydrate), 0.178 mg/ft² of sodiumacetate and 0.194 mg/ft² of alkyl phenoxy polyoxy ethylene glycol; ahardened gelatino silver iodobromo emulsion coated at a coverage ofabout 85 mgs/ft² of silver, 114 mgs/ft² of gelatin, 50 mgs/ft² of Dow620 carboxylated styrene butadiene latex, 4.56 mgs/ft² of propyleneglycol alginate and 0.55 mg/ft² of chrome alum (coverage as K₂ Cr(SO4)₂. 12 H₂ O); and an antihalo top coat of 300 mgs/ft² of gelatin, 175mgs/ft² of Dow 620 carboxylated styrene butadiene latex, 8.8 mgs/ft² ofpropylene glycol alginate, 1.2 mgs/ft² of dioctyl ester of sodiumsuccinic acid, 5.6 mgs/ft² of pyridiniumbis-1,5(1,3-diethyl-2-thiol-5-barbituric acid) pentamethine oxanol, 7.0mgs/ft² of 4-(2-chloro-4-dimethyl-amino benzaldehyde)-1-(p-phenylcarboxylic acid)-3-methyl pyrazolone-5 and 5.0 mgs/ft² ofbenzimidazole-2-thiol gold Au⁻¹ complex (as gold).

A film unit as identified above was exposed through the additive colorscreen to a step wedge. After a polyester cover sheet was superposedover the film unit it was processed, while being retained intact, byspreading a layer of processing composition less than about 1.2 milsthick between the anti-halo top coat layer and the cover sheet. Theprocessing composition was prepared by adding 0.4 ml of compound A to 10ml of the following formulation:

    ______________________________________                                        Water              79.02 g.                                                   Hydroxyethyl cellulose                                                                           0.84 g.                                                    Sodium hydroxide   10.04 g.                                                   Tetramethyl reductic acid                                                                        8.38 g.                                                    Sodium sulfite     0.97 g.                                                    Potassium bromide  0.73 g.                                                    4-aminopyrazolo (3,4-d)                                                       pyrimidine         0.019 g.                                                   ______________________________________                                    

After an imbibition period of about one minute the cover sheet wasstripped away and the maximum and minimum densities of the resultantimage were determined with a transmission densitometer. The values wereas follows:

    ______________________________________                                               Red         Green   Blue                                               ______________________________________                                        D Max    1.83          2.31    3.33                                           D Min    0.80          0.98    1.45                                           ______________________________________                                    

In another illustrative showing, a film unit was prepared as follows:the light sensitive element comprised a transparent polyester film basecarrying on one surface an additive color screen of approximately 1500triplets per inch of red, blue and green filter screen elements inrepetitive side by side relationship; a composite barrier structure madeup of an approximately 0.7 micron thick layer of polyvinylidene chloridecoated from a solvent, an approximately 1.0 micron thick layer ofpolyvinylidene chloride coated from water emulsion and an approximately0.3 micron thick layer of polyvinyl formal; a nucleating layer asdescribed in the previous example; an interlayer of 1.94 mgs/ft² ofgelatin, and 0.194 mg/ft² of alkyl phenoxy polyoxy ethylene glycol; ahardened gelatino silver iodobromo emulsion coated at a coverage ofabout 85 mgs/ft² of silver, 85 mgs/ft² of gelatin, 7.5 mgs/ft² ofpropylene glycol alginate, 0.41 mg/ft² of chrome alum (coverage as K₂Cr(SO₄)₂, and 0.61 mg/ft² of alkyl phenol polyglycol ether (average 9.5mols ethylene oxide) surfactant; and an antihalo top coat as describedin the film unit of the previous example with the exception that 22mgs/ft² of propylene glycol alginate were present.

The cover sheet comprised a 4 mil thick polyester support having a thincoating on one surface to prepare the support for coating. Coated on thesupport in the following order were:

(A) An acid providing layer formed by combining 60 parts by volume of a30% solution of the half butyl ester of ethylene maleic anhydride inmethyl ethyl ketone and 40 parts by volume of a solution of 5.7% ButvarB-72 (available from Monsanto), 63.3% ethyl acetate and 31% n-butanoland coating the mixture on the support to provide a dry coverage ofabout 2.45 mgs/ft² ; and

(B) A gelatin layer formed by coating a water solution containing 10%deionized gelatin, and 0.05% Emulphor ON-870 (available from AntaraChemical Co.) to provide a dry coverage of about 1 mg/ft².

The film unit as identified above was exposed through the additive colorscreen to a step wedge and processed while being retained intact, byspreading a layer of a processing composition less than about 3 milsthick between the cover sheet and the light sensitive element. Theprocessing composition was prepared by adding 0.5 ml of compound (B) to10 ml of the following formulation:

    ______________________________________                                        Water              82.36 g.                                                   Sodium hydroxide   7.265 g.                                                   Hydroxyethyl cellulose                                                                           2.811 g.                                                   Sodium sulfite     2.54 g.                                                    Tetramethyl reductic acid                                                                        3.17 g.                                                    Dodecyl-N,N-dipyridinium                                                      dibromide          1.78 g.                                                    4-aminopyrazolo (3,4-d)                                                       pyrimidine         0.016 g.                                                   5-bromo-6-methyl-4-                                                           azabenzimidazole   0.016 g.                                                   Thiazololidine-2-thione                                                                          0.035 g.                                                   ______________________________________                                    

After an imbibition period of about one minute the maximum and minimumdensities of the image were determined on a transmission densitometer.The values were as follows:

    ______________________________________                                               Red         Green   Blue                                               ______________________________________                                        D Max    1.58          1.69    1.64                                           D Min    0.29          0.31    0.38                                           ______________________________________                                    

When examined visually 17 days after processing no crystals wereapparent in the transparency. The image was stored under ambientconditions during the interim.

It will be apparent that the relative proportions of the subject silverhalide solvents and of the other ingredients of the processingcompositions may be varied to suit the requirements of a givenphotographic system. Also, it is within the scope of this invention tomodify the formulations set forth above by the substitution of alkalies,antifoggants and so forth other than those specifically mentioned. Wheredesirable, it is also contemplated to include in the processingcompositions, other components as commonly used in the photographic art.

The invention will now be described further in detail with respect tospecific preferred embodiments by way of examples, it being understoodthat these are illustrative only and the invention is not intended to belimited to the materials, conditions, process parameters, etc., recitedtherein. All parts and percentages are by weight unless otherwiseindicated.

EXAMPLES Preparation of N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)-ethylenediamine

A 250 ml three-neck flask, equipped with a magnetic stirrer, additionfunnel, thermometer and argon inlet was charged with a solution of 18.3g. (0.208 mol) of N,N'-methylethylenediamine in 70 ml of benzene. Asolution of 25.1 g. (0.417 mol) of ethylene sulfide in 10 ml of benzenewas added with stirring to the solution in the flask under argon whilemaintaining the temperature of the solution in the flask at 50°-55° C.The resulting clear solution was allowed to remain overnight at ambienttemperature, washed with two 5 ml portions of water and dried overmagnesium sulfate. The solvent was removed under reduced pressure and39.9 g. (97% yield) of a colorless oil was obtained.

The material is susceptible to air oxidation and therefore furtherpurification was not carried out. The material can be stored up to aweek under argon in a freezer without any significant deterioration.Since the compound has an extremely unpleasant odor and can cause severeskin allergy careful handling is necessary.

EXAMPLE I

Preparation of Compound B

A three neck liter flask equipped with an overhead stirrer, additionfunnel and argon inlet, and an oil bath was charged with 14.5 g. of a50% sodium hydride dispersion in oil (0.26 molar in NaH). Most of theoil was removed by repeated washings with petroleum ether carried outunder argon. In each washing about 15-20 ml of petroleum ether wereadded to the dispersion, the dispersion stirred briefly and allowed tosettle and supernatant liquid removed with a syringe. 520 ml ofspectrograde dimethylformamide were then introduced into the dispersionand the reaction flask was heated with the oil bath maintained at about95° C. When the internal temperature of the flask reached about 75° C.there was begun the dropwise addition, with vigorous stirring, of amixture of 27.08 g. (0.13 mole) ofN,N'-dimethyl-N,N'-bis(2-mercaptoethyl)ethylenediamine and 18.6 g. (0.13mole) of bis-2-chloroethylether in 40 ml dimethylformamide. Addition ofthe mixture was completed in about 2 1/2 hours. The temperature wasmaintained at about 80°-85° C. throughout the addition of the mixtureand for about 16 hours thereafter. Most of the solvent was removed invacuo with the bath temperature at about 70°-75° C. The resulting thicklight brown oil was dissolved in 300 ml of ethylacetate, washed withthree 20 ml portions of water and dried over magnesium sulfate. Removalof the solvent under reduced pressure gave 34 g. of a light brown syrup.¹³ C NMR and chromatographic analysis showed this to be a complexmixture of products.

A solution of 18 g. of the crude product in 200 ml of methanol wasformed and to it there were added 10.9 g. of silver thiocyanate inportions. Toward the end of the silver thiocyanate addition dissolutionof the silver salt became slow and a sticky material separated fromsolution. The mixture was stirred for about 15 minutes after which thesoluble portion was removed, diluted with 100 ml of methanol andfiltered through Celite 542 (a diatomaceous earth material availablefrom Johns Manville Co.). The filtrate was concentrated to 120 ml underreduced pressure and stored for two days in a refrigerator. Light yellowcrystals deposited during storage and these were collected, washed withmethanol and recrystallized from methanol twice at low temperature byfirst dissolving the crystals in excess solvent at 40° C. and thenconcentrating to about one-half the initial volume. The crystals werethen dried under high vacuum. A total of 8.5 g. of 1:1 compound B -silver thiocyanate complex, m.p. 147°-149° C. was recovered.Recrystallization of a small sample of this material gave essentiallycolorless crystals, m.p. 149°-150° C. C₁₃ H₂₆ N₃ OS.Ag requires 35.13%C,5.895%H, 9.46%N, 21.64%S and 24.27%Ag. Elemental analysis of thismaterial gave 35.03%C, 5.91%H, 9.50%N, 21.60%S and 24.43%Ag. Also NMRspectral data were consistent with a compound B - silver thiocyanatecomplex.

8.3 g. (18.7 moles) of the complex were dissolved in 100 ml of a 70:30(vol/vol) mixture of dichloromethane and ether and treated with hydrogensulfide gas to precipitate silver as silver sulfide. Bubbling ofhydrogen sulfide was continued until an aliquot of the supernatantsolution gave no precipate with hydrogen sulfide. The mixture was thenstirred for about 15 minutes, filtered through Celite 542 and thefiltrate was concentrated to a thick colorless syrup, presumably athiocyanic acid complex of ligand B. The free ligand, compound B, wasobtained from this material by the following alternative procedures:

(A) A column of a strongly basic, quaternary ammonium (polystyrene)type, anion exchange resin (Amberlite IRA-400) was prepared incarbonate-free water, washed with dilute sodium hydroxide and thenthoroughly with water until the eluent was not basic. An aqueoussolution of the above colorless syrup was passed through the column andwashing with carbonate-free water was continued until most of thematerial had been eluted. The combined washings were concentrated underreduced pressure. The residual syrup was dissolved in absolute ethanol,filtered through Celite 542 and the filtrate concentrated to provideabout 5 g. of compound B as a clear colorless syrup. The sample wasdried at 50° C. by pumping under high vacuum.

(B) Alternatively, the aqueous solution of the bisthiocyanic acidcomplex was treated with a stoichiometric amount of a 10% aqueoustetramethylammonium hydroxide solution and extracted with ethylacetateor dichloramethane. The organic layer was washed with water and driedover anhydrous sodium sulfate. Removal of the solvent gave compound B asa colorless syrup.

C₁₂ H₂₆ N₂ S₂ O requires 51.75%C, 9.41%H, 10.06%N, 23.03%S and 5.74%O.Elemental analysis gave 51.74%C, 9.39%H, 10.02%N and 22.84%S.

EXAMPLE II Preparation of Compounds C and D

A solution of 0.25 g. of compound A in 5 ml of tetrahydrofuran wasformed, cooled in an ice bath and to it was added dropwise over a periodof about 15 minutes a solution of 0.186 g. of p-nitrobenzoyl chloride in5 ml tetrahydrofuran. The solution was stored overnight in arefrigerator, warmed to 0° C. and then stirred at room temperature forabout four hours. The solvent was removed and the residue trituratedwith ice. A semi-solid was obtained and extracted with dichloromethane.The extract was washed with dilute sodium hydroxide until the aqueouslayer was slightly basic and then dried over sodium sulfate. Examinationof the product by thin layer chromatography on silica gel using a 20:1(vol/vol) ethylacetate-ethanol mixture as the eluent showed the productto be a mixture of the mono-(compound C) and diacylation (compound D)product as well as starting material.

The diacylation product, m.p. 196°-197° C. was separated byrecrystallization from absolute ethanol. The filtrate, upon removing thediacylation product, was concentrated. Examination of the concentrate bythin layer chromatography on silica gel using a 85:15 (vol/vol)benzene-methanol mixture showed it to contain primarily themonoacylation product (compound C) and the starting material along withminor impurities. The monoacylation product was isolated as a thicksyrup by chromatographing the product two additional times under thesame conditions. The NMR spectrum of the product was consistent withcompound C.

EXAMPLE III Preparation of Compound D

A suspension of 0.322 g. of the dihydrochloride salt of compound A in 5ml of benzene was treated with 2 ml of dimethylformamide to dissolvemost of the solid, followed by the addition of 0.28 ml triethylamine.Then a solution of 0.186 g. of p-nitrobenzoyl chloride in 2 mltetrahydrofuran was added dropwise and the mixture stirred overnight atroom temperature. The mixture was concentrated, diluted with 15 ml ofice water, extracted with three 15 ml portions of dichloromethane anddried over magnesium sulfate. The product was concentrated to give athick syrup which solidified when triturated with methanol at ice bathtemperature. The solid was filtered, washed with methanol and driedunder reduced pressure to give a white solid, m.p. 195°-198° C. The NMRspectrum was consistent with compound D.

EXAMPLE IV Preparation of Compounds E and F

A solution of 0.38 g. of compound A in 10 ml dry ether was formed andcooled in an ice bath. The solution was treated with etherealhydrochloric acid (HCl gas dissolved in ether at 0° C.) until thesupernatant liquid showed no turbidity upon additional treatment withethereal hydrochloric acid. A white solid (the dihydrochloride salt ofcompound A) separated from solution, was removed by filtration andwashed with ether.

To a stirred suspension of 0.32 g. of the dihydrochloride salt ofcompound A in 2 ml of 6% potassium hydroxide solution there was added0.23 g. of tosyl chloride. The mixture was warmed to a temperature of50°-60° C. for about 15 minutes and then cooled in an ice bath. Thesolid which formed was removed by filtration, washed with water andcrystallized from ethanol to provide colorless, needlelike crystals,m.p. 170°-172° C. The NMR spectrum of the material was consistent withthe ditosylate (compound F).

After removing the ditosylate the aqueous filtrate was extracted withdichloromethane and the extract dried and concentrated. The material wasthen chromatographed on silica gel using an 80:20 mixture ofethylacetate-ethanol as the eluent to separate the monotosylate(compound E) as a colorless syrup which solidified on standing at roomtemperature, m.p. 71°-73° C. The NMR spectrum of the material wasconsistent with the monotosylate.

EXAMPLE V Preparation of Compounds G and H

125 mg of compound A were dissolved in 1.5 ml of dichloromethane and tothe solution were added dropwise, with stirring, 0.05 ml of aceticanhydride. The mixture was heated under reflux for 6 hours and thenstirred overnight at room temperature. The solvent was removed and theresidue taken up in 25 ml of dichloromethane, washed sequentially with0.5 N hydrochloric acid, 3% sodium bicarbonate and water. The extractwas dried over magnesium sulfate and concentrated under reduced pressureto give the crude product mixture as a semi-solid. Crystallization fromabsolute ethanol gave colorless crystals, m.p. 145°-146° C. The NMRspectrum was consistent with compound G.

EXAMPLE VI Preparation of Compound I

To a suspension of 0.24 g. of a 50% sodium hydride dispersion in oil(which had previously been washed free of oil with petroleum ether) in15 ml of dimethylformamide was added 0.95 g. of mechlorethaminehydrochloride. To the resulting free amine were added 1.05 g. ofN,N'-dimethyl-N,N'-bis(2-mercaptoethyl) ethylenediamine in 5 ml ofdimethylformamide.

To a separate three neck flask there was added 0.5 g of a 50% sodiumhydride dispersion in oil and this was washed free of oil with petroleumether under argon. To this were added 50 ml of dimethylformamide and thesuspension was heated to 80°-90° C. The mixture of the two reactantsprepared above was then added dropwise with vigorous stirring over aperiod of about 25 minutes and stirring was continued at thattemperature overnight. The solvent was then removed under reducedpressure, the residue taken up in 25 ml of ethyl acetate, washed twicewith two 5 ml portions of water and dried over sodium sulfate. Removalof the solvent gave 1.4 g of a slightly colored syrup. ¹³ C NMR and thinlayer chromatographic analysis on silica gel using a 50:50 (vol/vol)mixture of ethylacetate-hexane showed this to be a mixture of products.Purification by column chromatography on silica gel gave 0.5 of compoundI which was characterized by ¹³ C NMR and mass spectrum (m/e=291, parention and 292 P+1).

A stirred solution of 116 mg of compound I in 5 ml methanol was treatedwith 66.4 mg of silver thiocyanate. After 10 minutes the mixture wasfiltered to remove traces of suspended material and the solvent removedunder reduced pressure to give a white crystalline solid, m.p. 160°-162°C. The product was crystallized from methanol by storing for severaldays in a refrigerator. Needle-like crystals formed and these werecollected by filtration and washed to give colorless needles, m.p.164°-165° C.

C₁₄ H₂₉ N₄ S₃ AG requires 36.75%C, 6.39%H, 12.25%N, 21.03%S and23.58%AG. Elemental analysis of the product gave 36.70%C, 6.35%H,12.29%N, 21.03%S and 23.74%AG.

EXAMPLE VII Preparation of Compound J

In a two-neck flask 0.24 g. of a 50% sodium hydride dispersion in oilwas washed free of oil with petroleum ether under argon atmosphere andthen 15 ml of dimethylformamide were introduced with a syringe. Thesuspension was stirred for 5 minutes and 0.89 g. of bis-chloroethylaminehydrochloride was added with stirring followed by the addition of 1.5 g.of N,N'-dimethyl-N,N'-bis(2-mercaptoethyl) ethylenediamine.

In a separate 3-neck flask equipped with an addition funnel there wasadded 0.5 g. of a 50% sodium hydride dispersion in oil which was thenwashed free of oil with petroleum ether under argon. Then 45 ml ofdimethylformamide were added and the suspension was stirred at atemperature of 80°-90° C. To the suspension was added dropwise over aperiod of 1.5 hours the reactant mixture described above. Stirring wascontinued overnight at that temperature and then for an additionalperiod at room temperature. Most of the solvent was removed underreduced pressure and the residue was taken up in 30 ml ethyl acetate,washed twice with 5 ml portions of water and dried over sodium sulfate.Removal of the solvent gave a clear light brown syrup.

The product was purified by column chromatography on silica gel using anethyl acetate-ethanol mixture for elution. NMR spectra of the productwere consistent with compound J.

EXAMLE VIII Preparation of Compound K

To a solution of 138 mg of compound J in 10 ml dichloromethane there wasadded dropwise, with stirring under argon at 5°-10° C., a solution of120 mg of p-nitrophenyl-chloroformate in 2 ml dichloromethane. Stirringwas continued overnight at room temperature after which it was dilutedwith 10 ml of dichloromethane, washed with dilute sodium carbonatesolution, then with water and dried over magnesium sulfate. Evaporationof the solvent under reduced pressure gave a light yellow syrup whichsolidified on standing.

The solid was chromatographed on a silica gel plate using a 90:10(vol/vol) ethyl acetate-ethanol mixture. The major band was removed andeluted with methanol. Removal of the solvent gave a solid which was thendissolved in ether, filtered through Celite 542, the filtrateconcentrated and the last traces of ether removed under reducedpressure. A pale solid m.p. 103°-107° C. was obtained. This solid wasrecrystallized twice from methanol to give a pale yellow crystallinesolid m.p. 109°-110° C., which was dried under reduced pressure.

C₁₉ H₃₀ N₄ O₄ S₂ requires 51.56%C, 6.83%H, 12.66%N, 14.49%S and 14.46%O.Elemental analysis of the product gave 51.63%C, 6.62%H, 12.56%N and14.39%S.

EXAMPLE IX Preparation of Compound L

In a 250 ml three neck flask equipped with an addition funnel, refluxcondenser and a serum cap there were added 1.01 g. of 50% sodium hydridedispersion in oil. The dispersion was washed free of oil by repeatedtreatments of petroleum ether under argon. Most of the petroleum etherwas removed with a syringe and the last traces removed by blowing withargon. Dimethylformamide (70 ml) was added and the suspension heated to70°-80° C. To the stirred suspension there was slowly added dropwiseover a period of 2 hours at a temperature of 85°-90° C., a mixture of2.1 g. of N,N'-dimethyl-N,N'-bis(2-mercaptoethyl) ethylenediamine and1.58 g. of bis-2-chloroethylsulfide in 15 ml dimethylformamide. Stirringwas continued overnight at 85°-90° C. after which the solvent wasremoved under reduced pressure. The residue was extracted with ethylacetate, washed three times with 5 ml portions of water and dried overmagnesium sulfate. The residue was concentrated to give a brown syrupand the last traces of solvent removed under reduced pressure. Theproduct was purified by chromatography with silica gel using ethylacetate as the eluent to furnish compound L as a pale-colored syrupwhich solidified under refrigeration.

C₁₂ H₂₆ N₂ S₃ requires 48.93%C, 8.89%H, 9.51%N and 32.66%S. Elementalanalysis of the product gave 48.88%C. 8.80%H, 9.38%N and 32.51%S.

Although the invention has been described with respect to variouspreferred embodiments thereof, it is not intended to be limited theretobut rather those skilled in the art will recognize that modificationsand variations may be made therein which are within the spirit of theinvention and the scope of the claims.

What is claimed is:
 1. A diffusion transfer photographic processcomprising the steps of:(a) reacting exposed silver halide in animagewise exposed photosensitive silver halide emulsion layer carried ona support with a silver halide developing agent in aqueous alkalinesolution; (b) reacting unreduced silver halide in said photosensitivesmulsion with at least one silver complexing compound to form a complexsilver salt which is soluble in said alkaline solution, said silvercomplexing compound being represented by the formula ##STR16## wherein Xis selected from the group consisting of oxygen, nitrogen, and sulfur:R₁ and R₂ are the same or different and are H. alkyl, hydroxyalkyl,alkoxyalkyl, ##STR17## wherein R₄ is H, alkyl, alkoxy or --NO₂ and R₅ isH, alkyl, alkoxy or alkoxyalkyl; provided that where X is --N--, R₃ isH, alkyl, hydroxyalkyl, alkoxyalkyl, ##STR18## wherein R₆ is H, alkyl,cyano or ##STR19## wherein R₇ is H or alkyl; (c) transferring saidsilver complex salt to a superposed image-receiving layer; and (d)reducing said complex silver salt on said image-receiving layer toprovide a silver image thereon.
 2. The process as defined in claim 1wherein R₁, R₂ and R₃ are independently selected from the groupconsisting of alkyl, hydroxyalkyl, and alkoxyalkyl having from two tosix carbon atoms.
 3. The process as defined in claim 1 wherein saidsilver complexing compound is represented by the formula ##STR20##wherein R₁ and R₂ are the same or different and are H, alkyl,hydroxyalkyl, alkoxyalkyl, ##STR21## wherein R₄ is H, alkyl, alkoxy or--NO₂ and R₅ is H, alkyl, alkoxy or alkoxyalkyl.
 4. The process asdefined in claim 3 wherein R₁ and R₂ are independently selected from thegroup consisting of alkyl, hydroxyalkyl, and alkoxyalkyl having from twoto six carbon atoms.
 5. The process as defined in claim 1 wherein saidsilver complexing compound is represented by the formula ##STR22## 6.The process as defined in claim 1 wherein said silver complexingcompound is represented by the formula ##STR23##
 7. The process asdefined in claim 1 wherein said silver complexing compound isrepresented by the formula ##STR24##
 8. The process as defined in claim1 wherein said silver complexing compound is represented by the formula##STR25##
 9. A photographic product comprising a support, a silverhalide emulsion carried on said support and a silver complexing compoundwhich is represented by the formula ##STR26## wherein S is selected fromthe group consisting of oxygen, nitrogen, and sulfur;R₁ and R₂ are thesame or different and are H, alkyl, hydroxyalkyl, alkoxyalkyl, ##STR27##wherein R₄ is H, alkyl, alkoxy or --NO₂ and R₅ is H, alkyl, alkoxy oralkoxyalkyl; provided that where X is --N--, R₃ is H, alkyl,hydroxyalkyl, alkoxyalkyl, ##STR28## wherein R₆ is H, alkyl, cyano or##STR29## wherein R₇ is H or alkyl.
 10. A photographic product asdefined in claim 9 wherein R₁, R₂ and R₃ are independently selected fromthe group consisting of alkyl, hydroxyalkyl, and alkoxy-Alkyl havingfrom two to six carbon atoms.
 11. A photographic product as defined inclaim 9, wherein said silver complexing compound is represented by theformula ##STR30## wherein R₁ and R₂ are the same or different and are H,alkyl, hydroxyalkyl, alkoxyalkyl, ##STR31## wherein R₄ is H, alkyl,alkoxy or --NO₂ and R₅ is H, alkyl, alkoxy or alkoxyalkyl.
 12. Aphotographic product as defined in claim 11 wherein R₁ and R₂ areindependently selected from the group consisting of alkyl, hydroxyalkyl,and alkoxyalkyl having from two to six carbon atoms.
 13. A photographicproduct as defined in claim 9 wherein said silver complexing compound isrepresented by the formula ##STR32##
 14. A photographic product asdefined in claim 9 wherein said silver complexing compound isrepresented by the formula ##STR33##
 15. A photographic product asdefined in claim 9 wherein said silver complexing compound isrepresented by the formula ##STR34##
 16. A photographic product asdefined in claim 9 wherein said silver complexing compound isrepresented by the formula ##STR35##